1. Field of the Invention
The present invention relates to a seating apparatus for a whipstock. More particularly the present invention relates to an expandable seat used to land a whipstock prior to the milling of a window through casing. The present invention also relates to a method for seating a whipstock in a parent wellbore.
2. Description of Related Art
In recent years, technology has been developed which allows an operator to drill a primary vertical well, and then later drill an angled lateral hole off of that vertical well at a chosen depth. The vertical wellbore, sometimes referred to as the parent wellbore, is cased with a string of casing and then cemented. In some cases, that parent wellbore is completed and hydrocarbons are produced from a downhole formation through that parent wellbore for a period of time before the lateral wellbore is created. In other cases, a lateral wellbore is completed along with or even in lieu of the parent wellbore.
In creating a lateral wellbore, an anchor, a slip mechanism, or an anchor-packer is typically set in the parent wellbore at a depth where deflection is desired. The anchoring device acts as a seat against which tools above it may be urged, including a whipstock. The whipstock is positioned in the casing above the anchoring device. Correct orientation of the whipstock is determined using a survey tool.
The whipstock is specially configured to divert milling bits and then a drill bit in a desired direction for forming a lateral wellbore. This process is sometimes referred to alternatively as sidetrack drilling, horizontal drilling, or directional drilling.
A stinger is typically located at the bottom of the whipstock which engages the anchor device or packer. In this respect, splined connections between the stinger and the anchor facilitate correct stinger orientation. The stinger allows the concave face of the whipstock to be properly oriented so as to direct the milling operation.
In some completions, it is desirable to seat the whipstock onto a tubular nipple in the casing string rather than using a packer. This avoids the necessity of running a separate anchoring device within the casing. Currently it is known to employ one or more seats, referred to as nipples, screwed into the casing string at the depth at which a lateral wellbore is to be drilled.
A substantial disadvantage exists with the use of currently-known casing nipples for seating a whipstock. The primary disadvantage is that, in drilling the parent wellbore, it is unknown precisely where a lateral wellbore will need to be deployed. Those of ordinary skill in the art will appreciate that downhole testing oftentimes is not conducted until after the parent wellbore is cased and cemented. Moreover, in many instances the drilling of a lateral wellbore does not take place until some extended period of time after the parent wellbore is completed. Therefore, some in the industry are incurring the time and expense of installing multiple casing seats within the casing string at various depths during the drilling operation. This increases the expense and complexity of the well completion process.
An additional disadvantage to the presetting of whipstock nipples within the casing string is that the orientation of each seat becomes fixed. In this respect, the orientation of the seats cannot be changed once they become part of the cemented casing string.
There exists, therefore, a need for a whipstock seat which can be set within casing at a time after the parent wellbore has been cased and cemented.
It is, therefore, one of the many objects of the present invention to provide a novel seat for landing a whipstock, wherein the seat can be set at a location in the casing of a parent wellbore after the casing has been cemented in place.
An additional object of the present invention is to provide a seat configured to receive a whipstock in such a manner that the whipstock is automatically oriented in a desired direction for directional drilling.
Yet an additional object of the present invention is to provide a seat for seating a whipstock which is expandable into the casing at a desired depth.
It is still an additional object to provide a method for seating a whipstock onto an expandable seat.
Additional objects and advantages will become apparent from the detailed description of the invention, below.
The present invention provides an apparatus for seating a whipstock, and a method for seating a whipstock within a cased wellbore.
The apparatus of the present invention comprises an expandable seat which is run into a cased wellbore at the lower end of a string of tubulars. The seat is releasably connected to an expander tool. At the appropriate depth, the expander tool is activated so as to expand a portion of the whipstock seat into contact with the casing. The connection between the expander tool and the seat is then released. The expander tool can then be reciprocated in a rotational and vertical fashion so as to expand the entire seat into a frictional connection with the cemented casing.
After the seat is expanded into position, the expander tool is removed from the wellbore. A whipstock is then run into the hole where it is landed onto the seat. The inner surface of the seat is dimensioned to receive the whipstock therein. Further, the inner surface is profiled so as to direct a key portion in the whipstock, thereby orienting the whipstock in the direction desired for drilling a lateral wellbore. In the preferred embodiment, a complete through-opening in the wall of the seat is formed to serve as the keyway.
The inner surface of the seat is optionally profiled for receiving dogs in the outer surface of the whipstock. This allows the whipstock to be seated more securely, and facilitates the removal of the run-in string without also pulling the whipstock. In this respect, a shearable or other releasable connection is employed between the run-in string and the whipstock so as to allow the whipstock to be released from the run-in string once the whipstock is seated. In one embodiment, the whipstock is releasably connected to a milling device so that milling of the casing may be commenced without incurring a trip out of the hole.